As a technique for forming color photographic images, it has conventionally been well known to imagewise exposure a silver halide photographic material (hereinafter referred to as "photographic material") containing therein a color coupler or couplers capable of causing a coupling reaction with an oxidation product of an aromatic primary amine compound and forming a dye, and to dip the exposed photographic material in a color developer containing the aromatic primary amine compound as a color-developing agent, to thereby cause coupling reaction between the oxidation product of the aromatic primary amine compound produced as a result of "development" of the exposed silver halide grains with the color-developing agent (reduction of silver ion of silver halide) and the color coupler or couplers, thus forming dyes and providing a color image.
In this technique, natural color can be reproduced based on subtractive color process by using at least three kinds of light-sensitive emulsion layers, respectively having blue sensitivity, green sensitivity, and red sensitivity, as photographic material-constituting light-sensitive emulsion layers and incorporating in respective emulsion layers color couplers capable of forming yellow, magenta, and cyan dyes.
Removal of developed silver produced simultaneously with formation of dye image and of remaining non-developed silver halide by respectively bleaching and fixing provides a stable color photographic image.
Color couplers to be incorporated in the photographic materials are preferably used in the form of being dissolved in a high-boiling solvent and dispersed in a hydrophilic colloid, so-called oil-protected form, for the purpose of enhancing stability of produced dye images. Most of color photographic materials at present used in the photographic field are of this type.
In recent years, there has been an increasing demand for improved productivity in the photographic field, and rapid processing of large quantities of prints has been the most important problem to be solved. As a means for solving this problem, it has been considered most effective to shorten the time of developing photographic materials, particularly the time of developing color photographic printing paper.
In order to shorten the developing time, it is necessary to provide as high a color density as possible within a limited developing time. As a means for this purpose, it may be considered effective to use color couplers showing as fast a coupling reaction rate as possible, to use a silver halide emulsion which can easily be developed and can provide a high amount of developed silver per unit coated amount, or to use a color developer which shows a fast developing rate.
In general, it is known that the coupling reaction rate depends upon both the reactivity of the color couplers used and the permeability of the color developing agent of aromatic primary amine compound into oil droplets (containing a coupler).
As is described above, the use of highly reactive color couplers is of extreme importance. However, in selecting couplers to be used in photographic materials, couplers which possess many excellent properties are required. For example, couplers are required not to adversely affect a silver halide emulsion incorporated in a photographic material together with the coupler (such as not to increase fog or not to reduce sensitivity during storage), to form dyes having a preferable hue from the standpoint of color reproduction, to form dyes with high stability to heat or light, to have a high stability to heat or light, and the like. Therefore, couplers selected as couplers having generally excellent properties do not necessarily have a sufficiently high coupling reactivity.
For these reasons, various techniques for accelerating permeation of a color-developing agent into oil droplets have been examined. Of such techniques, the technique of adding benzyl alcohol to a color developer to accelerate development is at present being widely employed for processing color photographic printing papers, due to its large coloration-accelerating effect.
In the case of using benzyl alcohol, its low solubility in water requires the use thereof together with a solvent such as diethylene glycol, triethylene glycol, alkanolamine, etc. However, such compounds inclusive of benzyl alcohol have high BOD (biochemical oxygen demand) or COD (chemical oxygen demand) values, which are environmental load values, and hence elimination of benzyl alcohol is preferable from the standpoint of reducing the environmental load.
In addition, even when the above-described solvent is used, it requires some time to dissolve the benzyl alcohol. Thus, it is preferable not to use benzyl alcohol from the viewpoint of reducing the work of preparing the processing solution.
Furthermore, when benzyl alcohol is entrained into a post-developing bath such as a bleaching bath or a bleach-fixing bath, it can cause production of leuco dyes of cyan dyes, thus causing reduction of color density. Still further, since benzyl alcohol decelerates the rate of washing out developer components, it sometimes adversely affects image stability of processed photographic materials. Therefore, for the above-described reasons, too, it is preferable not to use benzyl alcohol.
In general, color development has conventionally been completed in 3 to 4 minutes. However, it has been desired to shorten the processing time even further.
However, elimination of a coloration accelerator such as benzyl alcohol and shortening of developing time necessarily lead to serious reduction of color density.
In order to solve this problem, various color development accelerators (for example, compounds described in U.S. Pat. Nos. 2,950,970, 2,515,147, 2,496,903, 2,304,925, 4,038,075, 4,119,462, British Pat. Nos. 1,430,998 and 1,455,413, Japanese Patent Application (OPI) Nos. 15831/78, 62450/80, 62451/80, 62452/80, and 62453/80 (the term "OPI" as used herein refers to a "published unexamined Japanese patent application"), Japanese Patent Publication Nos. 12422/76 and 49728/80) have been proposed for use together, but sufficient color density still can not be obtained.
Further, the technique of incorporating a 3-pyrazolidone or its derivative is known by Japanese Patent Application (OPI) Nos. 50536/83, 26338/85, 26339/85, 158444/85 and 158446/85.
Still further, the technique of incorporating a color-developing agent (described, for example, in U.S. Pat. Nos. 3,719,492, 3,342,559, 3,342,597, Japanese Patent Application (OPI) Nos. 6235/81, 16133/81, 97531/82, 83565/82, etc.) has the defect that color development is decelerated or that fog is formed.
The following various techniques have been known as well as the above-described techniques as the method that benzyl alcohol is eliminated from a color developer or the amount thereof added thereto is reduced.
The technique of incorporating benzyl alcohol or the derivatives thereof together with high boiling solvent in the form of dispersion into a layer adjacent to the emulsion layer in order to prevent admixture thereof with coupler is described in Japanese Patent Publication No. 29461/74.
Further, the technique comprising color development with a color developer, washing immediately after the color development, and then bleach-fix with bleach-fixing solution containing metal complex salt of organic acid is described in Japanese Patent Application (OPI) No. 52058/80.
Still further, the technique of using 2-acylamino-5-ureidophenol-type cyan coupler is described in Japanese Patent Application (OPI) No. 31334/83.
Even further, the technique of using pivoloyl acetanilide-type yellow coupler, 3-anilino-5-pyrazolone-type magenta coupler and 2,5-diacylaminophenol-type cyan coupler in combination thereof is described in Japanese Patent Application (OPI) No. 200037/82.
Further, the technique of using a photographic coupler wherein a naphthalene ring nucleus is present at the linking position other than coupling position and the naphthalene ring nucleus has at least one hydroxyl group and at least one sulfonyl group or has at least one hydroxyl group and at least one sulfinyl group is described in Japanese Patent Application (OPI) No. 174836/84.
A yet further, the technique of using a coupler having a ballast group represented by the following formula: ##STR1## (wherein X represents a halogen atom or etc., l represents an integer of 1 to 4, and m represents 1 or 2) is described in Japanese Patent Application (OPI) No. 177553/84.
Further, the technique of using 4-mercapto-5-pyrazolone-type magenta coupler is described in Japanese Patent Application (OPI) No. 162256/85.
Further, the technique of effecting color development in the presence of compounds represented by the following formula (A) or (B): EQU R.sub.1 --O--R.sub.2 (A) EQU R.sub.3 --O--CH.sub.2).sub.n O--R.sub.4 (B)
(wherein R.sub.1 and R.sub.2 each represents an alkyl group, R.sub.3 and R.sub.4 each represents an alkyl group, and n represents 2 or 3) is described in Japanese Patent Application (OPI) No. 172042/85.
We, the inventors, have studied the above Japanese Patent Publication and Application (OPI)'s and have not been able to obtain a fully satisfactory result.
As is described above, no processes have been found for obtaining satisfactory color images in a short time by using a color developer which does not substantially contain benzyl alcohol.
On the other hand, as a technique for solving the above-described problems by accelerating development of a silver halide emulsion, it can be easily considered to increase the content of silver chloride in silver halides. However, an increase in the content of silver chloride involves the defect that reduction of sensitivity or formation of fog is liable to occur. In addition, for the purpose of increasing the amount of developed silver, it may be considered to increase the content of silver chloride as described above or to strengthen chemical sensitization. However, these steps may also cause formation of fog. Another technique for accelerating development involve reducing the grain size of silver halide emulsion. However, this technique has a serious defect of reduction of sensitivity. The technique of using a silver chloride emulsion is described, for example, in Japanese Patent Application (OPI) Nos. 95345/83, 232342/84, and 19140/85. According to this technique, when rapid processing is conducted using a color developer containing substantially no benzyl alcohol, such defect that harder tone cannot be obtained occurs.
Analysis by the inventors on the reduction of color density caused by substantially eliminating benzyl alcohol from the color developer has revealed the phenomenon that, when density of the dye is reduced, the amount of developed silver is also reduced. No improvement is found on this even when developing time is prolonged, which means that dead grains--silver halide grains not contributing to development in a limited development processing time using a substantially benzyl alcohol-free color developer--are produced. Such dead grains are considered grains having an extremely poor developing activity. They are produced due to some difference in properties of silver halide grains contained in an emulsion. Therefore, it would appear to be effective to use monodispersed silver halide grains in a silver halide emulsion, to thereby achieve uniform properties of respective grains, as disclosed or suggested in Japanese Patent Application (OPI) Nos. 48755/84, 26339/85 and 158446/85.
Experiments were conducted using silver halide emulsions containing highly monodispersed silver halide grains. However, though areas with an intermediate gradation are made contrasty and maximum density is raised to some extent, color-forming efficiencies in the shoulder part of the characteristic curve, which provides the density necessary for the reproduction of shadow areas in color prints, are insufficient, and hence such emulsions are still somewhat unsatisfactory for use in color photographic papers which are required to reproduce vivid tone from high-light areas to shadow areas.
It has been known in not only U.S. Pat. No. 4,446,228 but also Japanese Patent Application (OPI) No. 116347/86 that at least two kinds of monodispersed emulsions are mixed for the purpose of improving covering power or etc. However, these descriptions substantially relate to an X-ray photography, but are irrelevant to the color image-forming process of the present invention.